I appreciate that Blesta may be more for developers but that really is a restriction to many. Not everyone is going to find it accessible. And given the increased complexity, I think more and better documentation is really needed.
Nice to know that you can do things that Blesta DOESN'T allow you to do .
Kidding aside, as a 'non' developer, I've found making custom modules for our business needs has been fairly easy/straight forward. We have our own custom server management system and integrated it with our WHMCS with ease. I somewhat dread the idea of doing the same with Blesta and I would personally consider the extra hurdles to jump as a limitation.
All things said and done, ACTUAL developers do seem to prefer Blesta so perhaps it is the only real choice for more competent programmers :-).